1. Field of the Invention
The present invention relates to a bearing system and a spindle motor assembly adopting the same, and more particularly, to a non-contact journal bearing system which compositely uses magnetic repulsion and hydrodynamic pressure, and a spindle motor assembly adopting the same.
2. Description of the Related Art
A bearing system guides and supports a rotating object.
FIG. 1 is a cross-sectional view of a motor-integrated video head drum assembly adopting a conventional bearing system.
Referring to FIG. 1, a stator 7, a component of a motor, is installed on the upper portion of a base 6 in the center of which a fixed shaft 1 with a predetermined height, another component of the motor, is installed. Typical bearings 3 are installed at the upper and lower portions of the fixed shaft 1. An inner ring 31 of the bearing 3 is pressed on and fixed to the fixed shaft 1, and an outer ring 32 thereof is pressed on and fixed to the inner circumferential surface of a rotating body 2 penetrated by the fixed shaft 1. A rotor 8, a component of the motor, facing the stator 7 is installed on the lower portion of the rotating body 2.
In such a structure, the rotating body 2 rotates, as it is supported by the typical ball bearings 3. Each of a plurality of balls 33 of the ball bearing 3 is located in the cavity provided by two grooves with semicircular sections formed on the facing surfaces of an inner ring 31 and an outer ring 32 as shown in FIG. 2. In order to support an axial load and a load of a direction vertical to an axial direction, the ball 33 diagonally contacts the inner ring 31 and the outer ring 32 at a predetermined angle.
As described above, when the rotating body is supported by the ball bearing 3, the ball 33 and the inner and outer rings 31 and 32 contacting via the ball 33 become deformed due to mutual contact and rolling friction. Also, the rotation of the rotating body is unbalanced due to matching errors generated by processing imperfections of parts such as inner and outer rings, balls, etc. caused when the ball bearing is manufactured. Such an unbalanced rotation has been investigated and is known to cause irregular vibration due to various factors, in particular, non-repeatable run-out (NRRO). NRRO degrades the performance of a spindle motor for use in a high-density storage apparatus which requires super-accurate vibration. Even though the components of the ball bearing are manufactured by a super-accurate processing method to improve the vibration of the rotating body system, the durability of the rotating body system is deteriorated by abrasion and heat generation of the components due to friction caused by highspeed rotation. A ball bearing made of ceramic has recently been proposed, but the manufacture of the ball bearing is difficult because of the physical characteristics of ceramic, and the manufacturing cost is high.